Coupler for waveguides utilizing ferrimagnetic material for mode conversion



y 1967' R; s. ALFANDARI ETAL 3,32 8

COUPLER FOR WAVEGUIDES UTILIZING FERRIMAGNE'I'IC MATERIAL FOR'MODECONVERSION Original Filed Nov. 24, 1961 ELECTRIC VECTOR PLANE OFPOLARIZATION DIRECTION OF PROPAGAT'ON DIRECTION OF APPLIED MAGNETICFIELD BIAS In venlors R. S. Alfandafi R. Paucha'rd y awn-her A Mgtirneys United States Patent Ofiice 3,321,718 Patented May 23, 19673,321,718 COUPLER FOR WAVEGUIDES UTEIZING FERRIMAGNETIC MATERIAL FORMODE CONVERSION Roger S. Alfandari, Paris, Robert Panchard, St. Mande,

and Georges Pireher, Paris, France, assignors to Compagnie FrancaiseThomson Houston-Hotchkiss Brandt Continuation of application Ser. No.154,664, Nov. 24, 1961. This application Oct. 25, 1965, Ser. No. 515,286Claims priority, application France, Nov. 23, 1960, 844,801, Patent79,002 5 Claims. (Cl. 33321) This application is a continuation of ourprior application Ser. No. 154,664, filed Nov. 24, 1961, now abandoned.

The present invention relates to improvements in ferrite members forwave guides.

It has already been proposed to place a ferrite member against the wallof a wave guide in the vicinity of the place at which the electricalfield of the incident wave has zero amplitude, said ferrite member beingsubjected to an external magnetic field having a component at rightangles to the plane of polarization of said wave.

Such a ferrite member constitutes a directional coupler between twomodes of propagation viz: modes TE and TE They enable two fundamentalmodes to be coupled substantially completely.

However, a certain fraction of the incident energy entering this coupleris absorbed by reason of the dielectric losses in the ferrite member. Itis an object of the invention to avoid or substantially avoid theselosses.

We have discovered that these losses can be reduced by replacing part ofthe ferri-magnetic material of the ferrite member by a low-lossdielectric material with a sufficient specific inductive capacity(dielectric constant). The desired effect of the selective filter isfurther demonstrated, as long as the volume of the ferri-magneticmaterial is not below a relatively small minimum. Consequently, thequantity of this material which is used can be substantially decreased,by reducing either its length or its breadth or both at the same time.

Accordingly, the invention consists in a wave guide element forming adirectional coupler between two propagation modes of electromagneticenergy, wherein a member of dielectric material having small losses anda dielectric constant of the order of that of the ferri-magneticmaterial within said element, said two members having a joint actionupon the waves propagating in said element.

In order that th invention may be more clearly understood, referencewill now be made to the accompanying drawing, which shows one embodimentthereof by way of example, in perspective view.

Referring to the drawing, a member P is placed against a narrow wall ofa section of wave guide G of a directional coupler. This member P has arectangular cross-section and is constituted by two complementaryelements; a small ferrite member F, also of rectangular section in thisembodiment, and a larger member D of low-loss dielectr-ic material, theshape of which is the same as that of the member P, from which themember F has been removed.

The specific inductive capacity of the dielectric material constiutingelement D must be similar to that of the ferrimagnetic materialconstituting the ferrite member.

In a specific embodiment an alumina type ceramic was used, the losstangent of which is about and the specific inductive capacity of whichis about 9. (The specific inductive capacity of ferrite is about 10.) Anormal rectangular section wave guide, which can be employed in the Xband for a frequency of 10,000 megacycles (interior dimension 10.16mm./22.'86 mm.) has been used, the member P being in the form of astraight prism having a rectangular section, one side of which is lessthan or equal to the height of the wave guide as shown in the drawingwhereas the other has a width equal to some mm. The losses of thecoupler are then reduced in a ratio up to or in excess of 10.

It is clear that the means of application and embodiment hereindescribed have no limiting character and have been given only as anillustration of the invention.

What we claim is:

1. In a microwave coupling device including a rectangular wave-guidesection and a member comprising ferrimagnetic material, said memberbeing positioned in the waveguide section adjacent a wall thereof andbeing subjected to a magnetic field having a component normal to theplane of polarization of a microwave of one TE mode in said guidewhereby energy reaching one end of said device in the form of a wave ofsaid one TE mode will be transferred to the other end of said device inthe form of a wave of another TE mode, the improvement according towhich said member consists in part of a low-loss dielectric materialhaving a dielectric constant close to that of said ferrimagneticmaterial.

2. In a microwave coupling device including a rectangular waveguidesection and a member comprising ferrimagnetic material, said memberbeing positioned in the waveguide section adjacent a narrower wallthereof and being subjected to a magnetic field having a componentnormal to said narrower wall whereby energy reaching one end of saiddevice in the form of a wave of said one TE mode will be transferred tothe other end of said device in the form of a wave of another TE mode,the improvement according to which the major portion of said memberconsists of a low-loss dielectric material having a dielectric constantclose to that of said ferrimagnetic material.

3. In a microwave coupling device including a rectangular waveguidesection and a member comprising ferrimagnetic material, said memberbeing positioned in the waveguide section adjacent a wall thereof andbeing subjected to a magnetic field having a component normal to theplane of polarization of a microwave of one TE mode in said guidewhereby energy reaching one end of said device in the form of a wave ofsaid one TE mode will be transferred to the other end of said device inthe form of a wave of another TE mode, the improvement according towhich said member comprises a body of low-loss dielectric materialhaving a dielectric constant close to that of said ferrimagneticmaterial, said body partly surrounding said ferrimagnetic material anddefining therewith a generally parallelopipedic member having a majordimension extending parallel to the direction of wave propagationthrough the waveguide, the volume of said body being substantiallylarger than that of said ferrimagnetic material, and the losses in saidmember being several times less than those in an all ferrite membercapable of effecting a like transformation of mode.

4. The device defined in claim 3, wherein said dielectric materalcomprises an alumina-base ceramic.

5. The device defined in claim 4, wherein said ferrimagnetic materialhas a dielectric constant of the order of 10, and said low-lossdielectric material comprises a ceramic composition having a dielectricconstant about 9 and loss factor about 10*.

N 0 references cited.

HERMAN KARL SAALBACH, Primary Examiner. M. N'USSBAUM, AssistantExaminer.

1. IN A MICROWAVE COUPLING DEVICE INCLUDING A RECTANGULAR WAVE-GUIDESECTION AND A MEMBER COMPRISING FERRIMAGNETIC MATERIAL, SAID MEMBERBEING POSITIONED IN THE WAVEGUIDE SECTION ADJACENT A WALL THEREOF ANDBEING SUBJECTED TO A MAGNETIC FIELD HAVING A COMPONENT NORMAL TO THEPLANE OF POLARIZATION OF A MICROWAVE OF ONE TE MODE IN SAID GUIDEWHEREBY ENERGY REACHING ONE END OF SAID DEVICE IN THE FORM OF A WAVE OFSAID ONE TE MODE WILL BE TRANSFERRED TO THE OTHER END OF SAID DEVICE INTHE FORM OF A WAVE OF ANOTHER TE MODE, THE IMPROVEMENT ACCORDING TOWHICH SAID MEMBER CONSISTS IN PART OF A LOW-LOSS DIELECTRIC MATERIALHAVING A DIELECTRIC CONSTANT CLOSE TO THAT OF SAID FERRIMAGNETICMATERIAL.